332 



ARMATURE CONSTRUCTION 



to mount the armature on a pair of knife edges, as roughly 



indicated in Fig. 413. 

 The knife edges must 

 be set up absolutely 

 level with the aid of a 

 spirit-level, and should 

 also be parallel. When 

 the armature is placed 

 on them it will roll 

 until the heaviest part 

 is at the bottom, and 

 balance weights are 

 applied at a point 

 diametrically opposite 

 this. 



A better form of 

 balancing table is 

 given in Fig. 414. In 

 this type, accurately 

 ground and polished 

 rings are put on the 

 armature shaft, mak- 

 ing a very sensitive 

 bearing, and guarding 

 the shaft against any 

 damage that might be 

 caused if the knife 

 edges are rather sharp. 

 When the armature 

 has taken up a steady 

 position (with the 

 heaviest part lowest), 

 ,the balance weights 

 are applied at the 

 lightest part. These 

 balance pieces may 

 consist of small pieces 

 of lead or white metal 

 screwed on with one or 

 two screws ; or if suit- 

 able recesses are left on 



the spider to receive balance weights, the metal may be cast in. 



